mains hum on rf signal

You did not mentioned the power rating or supply voltage. Use a regulated power supply (first test it on bench PSU and see the result).

Sometimes the hum actually is a harmonic of 50/60Hz, and needs more research to solve the problem.

use good regulator.

thx all reply,

i use 110V in 60Hz

to power,

and regulator is 78L05 for 5V supply to RF

If you have a bench supply, did you check with it?. secondly, did you identify that this is due to supply, (i mean on battery it worked fine).

78L05 and 78xx regulators have quite poor supply rejection, you should use a better regulator, at least a LM317. It depends on your project, VCOs, receivers are very sensible to mains hum, but large signal amplifiers are not so sensitive.

Be careful with the ground traces layout and connection to voltage regulator to avoid loops and paths that "avoid" the voltage regulator.

Could also be:

- Ground loops;
- Magnetic induction on the surrounding components;

Also I have used with good results the old 723 instead of 7805; much better the old.

Mandi

Thx for your guy help

i am making a remote dimmer(use AC),

so i cannot test with bench supply(and i don't have other equipment),

and thx for the suggestion of using the other regulator

and thx for the PCB grounding suggestion .!:D